Field of the Invention
The present invention pertains to jointed concrete. More particularly, the present invention pertains to the use of hollow carbon steel dowels in jointed concrete pavement and methods of forming and using such dowels.
General Background
To prevent concrete pavement from cracking along random fracture lines, it is common to partially cut through new pavement to create intentional fracture lines. However, creating near planar fractures in pavement prevents the concrete from transferring any appreciable out-of-plane shear loads across such joints. Thus, to prevent adjacent sections of concrete from shifting out-of-plane relative to each other, metal dowels running parallel to the pavement are often positioned within the concrete across such joint lines before the concrete cures. Once the concrete fractures along the joint, the dowels transfer the shear loads between adjacent sections of concrete to thereby prevent relative transverse movement between such sections of concrete.
Most concrete pavement dowels are solid carbon steel cylindrical rods. Such dowels are fairly inexpensive and are cut from longer lengths of rod. Typically, long rods of carbon steel are shipped to a processing center or to a job site, where they are then batch cut to length for use as dowels. The batch cutting typically involves placing a plurality of rods (20 or more) in a basket or cradle style holder and thereafter cross-cutting the plurality of rods to length via a band saw. To reduce corrosion, carbon steel dowels may be galvanized, epoxy coated, or otherwise coated to reduce corrosion.
In rare situations requiring extremely long life pavement or involving pavement in abnormally corrosive environments, stainless steel dowels are used. In view of the relatively high cost of stainless steel compared to carbon steel, such stainless dowels are typically welded tube rather than solid rod. The added cost of forming the welded stainless tube is justified by the lower total material cost of the dowels. However, like the standard carbon steel rods, stainless steel tube dowels are typically batch cut from long cylindrical tubes of stainless steel that are shipped to a processing center or to a job site. In view of the inherent corrosion resistance of stainless steel, coating such stainless steel tube dowels with epoxy or otherwise coating such dowels is not necessary. It should be appreciated however that stainless steel tube dowels are significantly more expensive compared to carbon steel rod dowels.
Concrete pavement dowels can be placed in concrete in several ways. Prior to pouring the concrete, the dowels may be placed on baskets or cradles. The concrete can then be poured over the dowels, with the baskets or cradles holding the dowels near the center of the pavement thickness. Alternatively, it has been increasingly common to place the dowels into poured uncured concrete, thereby eliminating the need for baskets or cradles. The dowels can be placed in the uncured concrete by hand or in an automated manner via a concrete paving machine.
Concrete pavement dowels are also used to repair concrete pavement and to merge new concrete pavement to existing cured concrete pavement. In such situations, a vertical cut face of the cured concrete is either exposed or formed. Thereafter, a plurality of horizontal holes are drilled into the vertical face of the cured concrete and dowels are inserted into the holes. The dowels are longer than the depth of the holes and therefore protrude outward from the vertical face. New concrete is then poured over and around the exposed portions of the dowels in a manner forming a new section of concrete pavement. Once cured, the interface between the old and new concrete can be partially cut to form a fracture line. When fractured, the dowels will carry any shear loads between the old and new sections of concrete.